In perforation for forming a through hole on a laminated substrate such as a printed wiring board, in the case that the diameter of the hole is large, perforation is conducted by placing a drill directly on the substrate. However, in the case of a general-purpose substrate with a small-diameter hole, generally thin metal film such as aluminum foil and a layer of various water-soluble compounds are placed on the above substrate and the substrate is perforated using a drill, a gimlet or a puncher.
In the above methods, the film of a water-soluble compound is used to prevent slipping of the drill-bit part caused by unevenness on the surface of the substrate and to precisely place the tip of the drill on the desired location for the through hole part, that is, to secure preciseness of the processing position. Furthermore, the aluminum foil is used to prevent peeling of the copper face on the substrate when pulling out the drill after perforating the substrate, that is prevention of burn, along with problems such as clogging of the through hole part caused by heat generated in the through hole part and adhesion of shaving scraps, which occur when perforating. By using a laminate of the aluminum foil/water-soluble compound film, through hole processing is conducted efficiently. Moreover, the water-soluble compound film has the advantage of being removable from the substrate by washing the substrate with water after perforating.
Described below are known documents describing the water-soluble compound used for the above purpose. For instance, (1) JP-A-4-92488 and (2) JP-A-4-92494 disclose applying polyethylene glycol or polypropylene glycol on one face or both faces of a substrate. (3) JP-A-7-96499 discloses applying a water-soluble polymer comprising a polyalkylene oxide compound and polycarboxylic acid and/or a diisocyanate compound. (4) JP-A-10-6298 discloses applying a composition comprising the water-soluble polymer and a metal compound.
However, the disclosed arts (1) and (2) have problems when perforating the through hole, such as stickiness tends to occur on the surface of the water-soluble compound film and preciseness of the processing position for the through hole part decreases, especially under conditions of high water content such as a high humidity atmosphere. Also, when using the water-soluble compound as a film, the moldability is poor and forming into a sheet becomes difficult.
Also, there is room for improvement in the above disclosed arts (3) and (4), from the viewpoint of preciseness of the processing position when conducting perforation continuously using a fine drill with a drill diameter of 0.15 mm.
Furthermore, each of the disclosed arts (1)˜(4) need to be improved further in plating throwing power, that is plating uniformly when plating the interior of the through hole, which is one of the recent high demands regarding quality.